Experimental support for vimeo.com

Works by embedding the embeddable version of the video wich currently works
for almost all videos.
Some video authors place some restrictions on their embedded videos like no
seekbar oder fullscreen button. Therefore we include a provisorical fullscreen
button.
Clarify descriptions and titles of settings for upcoming vimeo support
Improve spf detection and handling

Spf is not touched anymore when using ie emulation because it works just fine there.
Also using a more general approach with works without changes after the page has
been changed with spf by lokking at all click events and determining if they
came from a link element.